The present invention relates generally to wafer handling systems. Processing of semiconductor wafers generally requires transportation of wafers from one process station to another. Due to the sensitivity of semiconductor devices to contamination by particulates, it has become common practice to transport wafers in enclosed containers, referred to as front opening unified pods (FOUPs). The term, “FOUP” is used herein to broadly refer to containers having a front opening that are configured to transport substrates to and from process tools. The FOUP door mates with a port door of a processing unit, and the doors are removed providing access by the processing equipment to wafers held within the FOUP.
FIG. 1 illustrates a conventional 300 mm FOUP 20, which includes a mechanically openable FOUP door 22 and a shell 24, which together, defines a sealed environment for storing one or more workpieces located therein. FOUP door 22 includes a front face 31 with two latch key receptacles 33.
FIG. 2 illustrates a conventional 300 mm load port assembly 23 for transferring wafers between the FOUP 20 and a process tool 28. Load port 23 attaches to the process tool by a box opener/loader-to-tool standard interface (BOLTS) plate 36 that has an aperture 18. The load port 23 includes, among other things, a container advance plate 25 and a port door 26. In order to transfer the workpieces between FOUP 20 and process tool 28, FOUP 20 is manually or automatically loaded onto advance plate 25 so that front surface 31 of FOUP door 22 faces front surface 30a of port door 26 while FOUP 20 is seated on advance plate 25. Port door 26 occludes aperture 18 when in the closed position illustrated in FIG. 2.
The front surface 30a of port door 26 includes a pair of latch keys 32 that insert into the corresponding latch key receptacles 33 of FOUP door 22 as FOUP 20 is advanced towards the port door 26. An example of a door latch assembly within a FOUP door adapted to receive and operate with latch keys 32 is disclosed in U.S. Pat. No. 4,995,430, entitled “Sealable Transportable Container Having Improved Latch Mechanism,” which is assigned to the Asyst Technologies, Inc., and is incorporated in its entirety by reference herein. In order to latch FOUP door 22 to the port door 26, FOUP door 22 is seated adjacent port door 26 so that vertically oriented latch keys 32 are received within latch key receptacles 33.
In addition to decoupling FOUP door 22 from the FOUP shell, rotation of the latch keys 32 also locks the keys into their respective receptacles 33; coupling FOUP door 22 to port door 26. A conventional load port includes two latch key 32, each of which are structurally and operationally identical to each other.
Advance plate 25 often includes three kinematic pins 27, or some other registration feature, which mate within corresponding slots on the bottom surface of FOUP 20 to define a fixed and repeatable position of the bottom surface of the FOUP on advance plate 25 and load port assembly 23.
Referring to FIG. 3, advance plate 25 is translationally mounted to advance the FOUP 20 toward and away from the load port 30. Once a FOUP 20 is detected on the advance plate 25 by sensors in the load port assembly, FOUP 20 is advanced toward load port 30 in the direction of arrow A-A until front surface 31 of FOUP door 22 is proximate front surface 30a of port door 26 so that the flange of FOUP 20 forms a proximity seal with BOLTS plate 36. The proximity seal provides a small space between the BOLTS plate surrounding the port door and the FOUP shell flange at the front edge of the FOUP shell after the pod has advanced. This space allows air 19, which is at a higher than ambient pressure within the process tool to sweep away any particulates and prevent particulates from coming to rest on the flange. The proximity seal also ensures that particulates and other contaminants cannot enter the tool or the FOUP. The higher than ambient pressure is provided by a filter/blower system (not shown) attached to process tool 28 (FIG. 2).
It is desirable to bring the front surfaces of FOUP door 22 into contact with the front surface of port door 26 and maintain contact to trap particulates between the doors. Once the FOUP and port doors are coupled, horizontal and vertical linear drives within the load port assembly move the FOUP door 22 and port door 26 together into the process tool 28 so that wafers may thereafter be transferred between the interior of the pod 20 and interior of process tool 28. In the open position, port door 26 is translated away from aperture 18 so that it no longer occludes aperture 18. For example, port door 26 and FOUP door 22 may be moved in and then down alongside an interior surface of BOLTS plate 36.
Regardless of the desired relative positions of the FOUP and port doors after FOUP advance, it is necessary to precisely and repeatably control this relative positioning to ensure proper transfer of the pod door onto the port door and to prevent particulate generation. In order to establish the desired relative positions, conventional load port assembly systems rely on the fact that the kinematic pins establish a fixed and known position of the FOUP on the load port assembly so that, once seated on the kinematic pins, the FOUP may simply be advanced toward the load port a fixed amount to place the front surfaces of the respective doors in the desired relative positions.
Many of the components of the load port 30, such as the BOLTS plate aperture 18, the port door 26 and the container advance plate 25, are fixed components—cannot be adjusted. A 300 mm load port 30 is designed to operate only with 300 mm pods 20. Thus, there is a need for a load port that can accommodate and operate with various sizes of FOUPs.